A case series and literature review of infections due to Myroides spp.: identification of contributing factors and emerging antibiotic susceptibility trends

Introduction. Infections forby Myroides spp. can lead to significant morbidity and mortality, particularly in immunocompromised patients with underlying co-morbidities. Recent reports have highlighted its intrinsic and acquired drug resistance, making it a particularly challenging infectious agent to combat. Methods. Myroides spp. isolated and reported in clinically significant urine samples were considered for the study. Identification of the organism was done via the VITEK 2C system. Antibiotic susceptibility testing was done using both manual and automated methods following Clinical and Laboratory Standards Institute (CLSI) guidelines. Existing literature was searched on MEDLINE using PubMed. Results. We present a series of five catheter-associated urinary tract infections due to Myroides odoratimimus , with sensitivity to only minocycline. This is the first case from Western India, and the third case in the existing literature that shows Myroides sensitivity only to minocycline. Our literature review is the first to systematically describe contributory factors to infection, allowing us to devise a clinically relevant tool that delineates contributory factors and efficacious drugs in Myroides spp. infection. Conclusion. Myroides spp. infections, previously considered rare and opportunistic, need cognizance and diagnostic suspicion especially in particular associated conditions.


CASE PRESENTATION
All urine samples received in the department of microbiology having significant bacteriuria for Myroides spp. were included in the study. For all cases, identification of the organism was done via the VITEK 2C system (bioMérieux). Antibiotic susceptibility testing was done using both manual (Kirby Bauer for disc diffusion and E-test for MICs) and automated (VITEK 2C) methods, following Clinical and Laboratory Standards Institute (CLSI) guidelines. Each isolate was sent to a reference laboratory for species identification using the matrix-assisted laser desorption ionization -time of flight (MALDI-TOF) Biotyper Sirius system (Bruker Daltonics). Sample size calculation using a power analysis was not done since this is a prospective observational study.

Case 1
A 48-year-old male presented to the emergency department in an unconscious and intubated condition with a suspected brain injury. He was a known case of hypertension with type 2 diabetes mellitus and was on regular medications for the last 2 years. Magnetic resonance imaging of the brain revealed intracranial bleeding, following which he was immediately taken in for craniotomy. Requisite pre-operative preparation, including urinary catheter placement, was carried out. On the fourth day of the surgery, the patient experienced bouts of fever and increased white blood cell (WBC) counts. A urine culture was sent to the microbiology laboratory before empirical therapy was begun with intravenous ceftriaxone. Cultures reported Myroides spp. sensitive only to minocycline, and species identification yielded M. odoratimimus as the causative organism. Administration of minocycline resulted in an improvement in WBC counts, and urine cultures sent on the seventh day of surgery returned negative. This was our index case of Myroides spp. The patient's condition worsened and eventually proved fatal, although not attributed to Myroides infection.

Case 2
A 29-year-old female who was a case of post-partum haemorrhage (PPH) and gestational diabetes was brought into our centre in an intubated condition. The patient developed abdominal pain with oliguria and altered sensorium 4 days after her normal vaginal delivery, following which she was transferred to our hospital and catheterized on admission. Based on abnormal baseline laboratory parameters on arrival, the patient was immediately moved to the intensive care unit (ICU). An emergent abdominal computed tomography (CT) scan revealed abdominal wall cellulitis with cystitis, and empiric therapy with intravensour piperacillin-tazobactam was begun for the same. Cultures on day 0 and 6 revealed no growth. On day 9 of her hospital stay, a fever spike was noted for which investigations were requested, with urine microscopy revealing pyuria. A urine culture was sent to the microbiology laboratory for further evaluation, revealing extensively drug-resistant Myroides spp. growth with sensitivity to only minocycline. The antibiotic minocycline was added to ongoing treatment for 7 days and counts resolved to within normal limits.

Case 3
A 41-year-old haemodynamically unstable diabetic male patient was referred to our hospital after having undergone multiple procedures including placement of a double-J (D-J) stent for a previous ureteric stricture and an emergent tracheal tube insertion. He presented with right-sided pleural effusion and was a known case of tuberculosis receiving modified anti-tubercular therapy, due to altered liver and kidney function. On admission, initial laboratory investigations revealed raised procalcitonin values, and a provisional diagnosis of sepsis and tubercular empyema was made. He was then moved to the ICU and catheterized for monitoring of kidney function. The patient had a fever spike on the eighth day, with urine microscopy revealing pyuria. A urine culture was sent to the laboratory and extensively drug-resistant Myroides spp. were isolated which were only sensitive to minocycline. Urine infection subsided by day 7 of minocycline administration and repeat cultures showed no further growth after cessation of treatment.

Case 4
A 55-year-old male was referred to our centre, having been admitted for breathlessness of sudden onset for 3 days. He arrived in an intubated and unconscious condition and was catheterized on ICU admission, revealing an oliguric state. He was a known case of type 2 diabetes mellitus for 7 years and hypertension for 2 years treated with insulin and antihypertensive medications. On initial workup and examination, a diagnosis of acute chronic kidney disease, lower respiratory tract infection, cardiogenic shock and multiorgan failure was made. Emergent treatment was begun. Ultrasonography of the abdomen revealed right-sided pleural effusion and bilaterally raised renal echogenicity. Initial blood and urine culture reports yielded no growth. On day 8 of admission, a fever spike was noted with raised WBC counts and pus cells on urine microscopy. Urine cultures were sent to guide empiric therapy and Myroides spp. were reported with susceptibility only to minocycline. The treatment plan was updated, and minocycline was administered for 7 days. Repeat cultures reported no growth and counts returned to normal. However, the condition of the patient deteriorated, and he died due to complications not attributable to the infection.

Case 5
A 69-year-old male was admitted to the emergency department with oliguria for the past 20 days and recent onset of disorientation and appetite loss over the previous 24 h. He was a known case of hypertension, type 2 diabetes, and chronic kidney disease for the last 5 years with a D-J stent in place. The patient was primarily managed in the emergency department where he was intubated, catheterized and then moved to the ICU. After further evaluation, a provisional diagnosis of acute liver failure and acute kidney injury with obstructive uropathy was made. Within 2 days of catheterization, the patient had a fever spike and raised WBC counts. Samples were sent for urine culture, which reported multi-drug resistant Myroides spp. Susceptibility was noted only to minocycline, similar to all our other cases. After administration of minocycline for 7 days, repeat cultures revealed no growth.

LITERATURE REVIEW
We conducted a literature search on PubMed using a mix of controlled terms and free text searching, with the string '((Flavobacteriaceae Infections) AND Myroides) OR (Myroides AND Infections)' which yielded 72 results. Papers of English language that presented clinical Myroides spp. infection were considered for inclusion. Forty-two papers describing a total of 97 cases were included (Table 1).

DISCUSSION
Our study is the latest in a series of recent studies that have found Myroides spp. to be almost pan-drug resistant [13,15,24,25,28,30,[35][36][37]. This is the first case from Western India, and the third case worldwide that shows Myroides sensitivity only to minocycline [24,35]. Analysis of the trends behind the occurrence of Myroides infection revealed a wide swathe of possible causes, but a trend emerged with infections occurring in hospitalized patients. Our case series (Table 2) is similar to other cases [16,19] in that there was a cluster of healthcare-associated urinary tract infections in patients with multiple comorbidities. All five cases had an indwelling device and were diabetic, pointing to these two being possible contributory factors to infection. Further investigation of contributory factors in the pre-existing literature revealed similar aetiologies in numerous cases. We elucidate this in Table 3, a clinically useful tool that portrays, at a glance, the risk factors for Myroides infection and drug classes most likely to be effective in treatment. This can help guide clinicians to suspect Myroides infection and initiate appropriate antibiotic therapy while keeping in mind local sensitivity patterns.
Myroides has classically been considered a ubiquitous organism and an opportunistic pathogen associated with infection only in immunocompromised patients (Table 1) or those having multiple comorbidities [34]. Cases due to animal exposure have been reported [20,22] and unsanitary environmental exposure via water or soil has been suspected as a contaminant [7,9,18,21,34,[38][39][40]]. Yet, attempts at identifying the source of this infection in nosocomial settings have been largely unsuccessful [16,19]. Of note is that infections in immunocompetent individuals are increasingly appearing in the literature [8-10, 14-16, 18-21, 24, 25, 27, 31, 32, 41, 42]. This throws into question the clinical presumption that Myroides infection is always opportunistic, and due diligence needs to be given to this emerging extensively drug-resistant pathogen.
Initiating appropriate treatment for Myroides infection is challenging due to resistance to commonly used antimicrobial agents. Myroides can auto-aggregate and co-aggregate to form biofilms and have strong adherence and hydrophobicity [23,26]. These properties along with chromosomally encoded beta-lactamases are hypothesized to confer drug resistance to most Myroides species [43]. More research is needed to elucidate the exact mechanisms of resistance in this organism [44,45]. Antibiotic susceptibility testing on our isolates using the VITEK 2C system revealed resistance to penicillins, cephalosporins, norfloxacin, ciprofloxacin, aztreonam, amikacin, gentamicin, imipenem, meropenem, colistin and polymyxin. Susceptibility only to minocycline was seen.
The emergence of such extensive drug resistance led us to analyse the existing literature for trends in risk factors and antimicrobial sensitivity, which resulted in the development of the clinical tool presented (Table 3). All papers retrieved through the literature search were used to mine data, and this gave startling results. The five most likely risk factors -indwelling catheters/devices, prolonged hospitalization, invasive/surgical procedures, diabetes and chronic kidney disease -were present in 56, 36, 35, 21 and 12 % of cases respectively. This finding underlines the high chance of infection that these risk factors confer on patients. Targeted therapeutic options were selected if they were sensitive in at least 50 % of the studies in which they were reported. Antibiotics that were not reported in at least three papers were not included, and intermediate sensitivity was not factored into the analysis. This led us to elucidate the top five therapeutic options that are useful in Myroides infections. Minocycline, though having the highest sensitivity percentage of 100 %, was placed at the end of the table since it was reported in just four studies, in contrast to the average of 10 studies for other antibiotic choices. More case reports which include minocycline in their antimicrobial susceptibility testing are required before it can be recognized as the drug of choice. Spanik et al. [8] found that source removal via changing catheters led to the resolution of Myroides infection without specific antimicrobial therapy. This therapeutic modality can be explored in subsequent studies. Timely and appropriate identification of Myroides, through antimicrobial testing and antibiotic susceptibility testing to better guide therapeutic decisions and interventions, is imperative, given their potential to cause outbreaks, non-healing of wounds and prolonged duration of hospital stay.
There are a few limitations of the present study. While conducting the literature review, we restricted our search to only MEDLINE. Expanding the scope of the search will yield additional cases, yet were beyond the scope of this study. A significant number of cases retrieved were of urinary tract infections, including our own, which could explain the high prevalence of catheterization and its subsequent association with Myroides infection. Future research in this area should aim to systematically review all available reports to glean information existing in different databases.

Funding Information
No funding was received for this study.